Trailer load balance is a critically important element to towing safely; too little tongue weight and you will get sway, and too much tongue weight and you get other adverse effects. The optimum is 10-15% of the gross trailer weight (the trailer weight plus the load) and this can be adjusted by moving your load foward/rearward until optimal. There's a few good articles online about measuring trailer tongue weight, so please Google for those if you're unsure. Video credit: Twitter user OPCVC, and